1. Field of the Invention
The present invention relates to image processing apparatus and method for reading a document sheet image and processing image data derived therefrom.
2. Related Background Art
In the field of the image processing apparatus, it has been known to read a document sheet by an image input unit, convert it to an electrical signal, apply image processing to the signal by an image processing unit and record it as an image by an output unit such as a laser beam printer. In a certain image processing apparatus, an image memory unit is provided in the image processing unit so that the document sheet once read by the image input unit is outputted to the laser beam printer from the image memory unit a plurality of times to form a plurality of sheets of image.
Further, it has been proposed that an image compression unit and an image decompression unit are built in before and after the image memory unit to attain effective operation of the image memory unit and this technique is being used in an application of electronic sorter for example.
On the other hand, an image compressing method which provides high efficiency and no degradation of quality is desired. To this end, the MH coding method and the Q-Coder which makes use of arithmetic coding have been known.
In the prior art digital copying machine, a document sheet is fed onto a plate glass by a document sheet feeder and stopped thereat, an optical system under the platen glass is moved to read an image of the document sheet, the read image of the document sheet is copied onto a record sheet and the document sheet is ejected from the platen glass. Such a digital copying machine is provided with a memory for storing image data representing the read image of the document sheet and image data outputted from a computer so that the image data stored in the memory is sequentially read to make records.
In order to improve a record processing speed of such a copying machine, moving read in which the document sheet is moved is preferred to stationary read in which an optical system is reciprocally moved.
However, the amount of data compressed by the compression method described above is not known until the compression is completed, so that when the memory becomes full during the moving read of the document sheet, the document sheet being read at that moment and the subsequent document sheet will be moved past the read station, and hence it is necessary to stop the operation of the apparatus and return by a user the document sheet which were moved past the read station without being copied to a feed unit of the document sheet feed unit. On the other hand, if the document sheet feed is constantly controlled to read the next document sheet after the completion of the output of one sheet of image data from the memory, the high speed operation cannot be attained and the productivity is lowered.